In general, a bill processing apparatus, which is one of the embodiments of the paper sheet processing apparatus, is incorporated into a service device such as a game medium rental machine installed in a game hall, a vending machine or a ticket-vending machine installed in a public space, or the like which identifies the validity of a bill inserted from a bill insertion slot by a user and provides various types of products and services in accordance with a value of the bill having been judged as valid.
Recently, it is also seen that a coupon ticket or the like having an equivalent economic value to that of a bill is issued in a game hall and processed by a bill processing apparatus which handles a regular bill. As such a coupon ticket, what has a bar code printed on a paper sheet (thermal paper) formed in the same size as that of a specific bill (typically, United States dollar bill) is known (i.e., a coupon ticket with a bar code) and it is possible for a user to be provided with equivalent services to those by the bill when the issued coupon ticket with the bar code is inserted, in the same manner as the bill, into the insertion slot of the bill processing apparatus which processes the bill.
Meanwhile, in such a way of using the bill processing apparatus, it is necessary for the abovementioned bill processing apparatus to be configured to be capable of judging the authenticity of the bill as well as such a bar-coded paper sheet. As such a bill processing apparatus, for example, Patent Document 1 discloses a configuration that a sensor device for reading a bill or a bar-coded paper sheet inserted into a bill insertion slot is installed in a bill traveling route.
This sensor device has optical sensors which are provided alongside a traveling route, and each of the respective optical sensors has a structure in which a light emitting diode and a light receiving transistor are installed in parallel in a case, and is configured to receive a light reflected on the bottom surface and top surface of each bill. Therefore, when the respective light emitting diodes of the optical sensors provided in parallel emit lights simultaneously, there is a concern that each light receiving transistor may be affected by the lights from the other light emitting diodes.    [Patent Reference 1] Japanese patent No. 3320806